Tuning indicator system



Patented July 5, 1938 einen PATENT orties TUNING INDICATOR SYSTEM Kenneth A. Chittick, Haddonield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 30,

6 Claims.

'The present invention relates to multi-wave band receivers and, more particularly, to tuning or resonance yindicator systems therefor. The present invention has for its object to provide an improved tuning or resonance indicator system wherein a uniform tuning response or resonance indication over a relatively wide tuning range including a plurality of wave bands, may be derived.

Heretofore, in providing tuning indications in response to received carrier waves or signals in a multi-wave band receiver, a differing degree of response has been obtained in one wave band as compared with that in another, because of inherent Acircuit connections tending to make the tuning indications weaker on the higher frequency orshorter wave bands. It is, therefore, ani object of the present invention to provide means havinga uniform tuning response as a tuning indicator, whereby this operating characteristic may be overcome.

It lis a further object of the present invention, to provide a tuning indication system of the above character wherein a tuning indicator tube of theV electronic, grid-controlled type known commercially as the Magic eye, which is provided by the commercially available RCA 6E5 tube, may be used.

As is known, the deflection on the indicating screen of a tuning indicator tube of the above type, is proportional to the voltage impressed upon the control grid of the amplifier portion of the -tube :It is also known -that the deflection or tuning 'indication as normally provided in commercial .carrier wave and with a high degree of selectivity,

whereby the indication is produced only when the receiver is tuned correctly to the desired carrier wave or signal.

In carrying out the objects of the invention, a tuning indicator tube circuit is provided in connection witha separate intermediate frequency amplifier channel which controls the deflection ofthe indicating portion of the tube, the intermediatefrequency amplifier further including a 55 f sharply tuned coupling transformer.

1936, serial No. 88,176

(o1. 25o- 2m With this circuit, the indicator tube will not begin to defiect until within approximately five kilocycles of the center of the carrier. The maximum deflection is very sharp and occurs only on the exact center of the carrier Wave. The broadness of the Magic eye tuning is thus eliminated, and the operator of the receiver is enabled to tune the same to exact resonance.

A further object of the present invention is to provide a tuning indicator system in which the sensitivity of the indicator device may be adjusted for conditions which obtain in any given locality in which the receiver is used, and for loss of sensitivity because of aging ofthe tubes and circuit elements. It will be appreciated that this feature is desirable, since the receiver may be operated in some cases in a metropolitan district and in the vicinity of a broadcasting station, and in other cases in remote portions of the country, at extreme distances from broadcasting stations,and for compensating for aging of the circuit elements and for differences in location, a sensitivity adjustment of the tuning indicator tube is desirable.

The invention will be better understood from the following description, when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

VIn the drawing, Fig. 1 is a schematic circuit diagram of a portion of a superheterodyne receiver embodying the invention; and

Fig. 2'is a schematic circuit diagram showing a modification of a portion of the circuit of Fig. 1.

Referring to the drawing, an intermediate frequency amplifier tube is indicated at 5, and is coupled with an intermediate frequency coupling transformer 6 to receive amplied signals from preceding usual tuning and frequency changing portions of the receiver. This portion of the receiver is not shown, for the reason that such receivers are well known and understood, and the omission of the input end thereof serves to simplify the drawing.

Intermediate frequency signals, amplified by tube 5, are applied through an output coupling transformer l, to a second detector tube 8, which includes two diode rectiers, in the present example, one of which is used for initial bias and the other of which is used as a detector and for automatic volume control purposes.

The detector diode is indicated by the anode 9 and the cathode l0, while the bias control diode is indicated by the anode Il and the cathode l2,

the heater for the cathodes being indicated at I3. This tube may be of the RCA 61-16 type.

The detector diode circuit includes the tuned secondary I4 of the intermediate frequency transformer 1, which is connected between the diode anode 9 and cathode I0, through an output resistor I5-I6, with the'cathode end thereof connected to ground as indicated at I1.

Automatic volume control potentials are applied to an automatic Volume control lead I8 from the diode circuit, through a lter comprising a series resistor I and a by-pass capacitor 20.

The diode output resistor is also provided with a shunt by-pass capacitor 2|.

Audio frequency signals are derived Yfrom the diode output resistor by a tap connection 22, having an audio frequency output lead 23. In the absence of signals, a biasing potential is supplied to the lead I8, to establish thereon a nega-l tive potential with respect to ground suflicient for normal biasing of .therreceiving tubes. This potential is derived from a series bleeder resistor 25-26-21 connected between a negative supply' lead 28. and ground 29. l Y

A tap point 3&3l on the b-leeder resistor is connected through a lead 3I and a filter comprising a series resistor 32 and by-pass capacitor 33, to the cathode I2 of the bias supply diode. The anode II of the bias supply diode is connected through a lead 34 with the bias supply lead I8.

It will be seen that the potential existing between the tap point 30 and ground 29, in connection with the bleeder resistor, is applied to the lead I8 through the ground connection I1, resistors I6, I5 and I9, and causes current to flow through the diode II-I2 and the resistor 32, byv

way of lead 3l, to the terminal at 30. It will also be seen that the current flows through the diode output resistor I5-I6, thereby providingr an initial biasing potential to the lead I8. In the presence of a received carrier wave, the diode S-I 0' causes current to flow through the output resistor I5-I6, and as soon a-sthe drop in potential increases above that established by the initial biasing rectifier, the received carrier wave serves to control the potential applied to the lead I8, and thereby provides automatic biasing potentials for the receiving system. Y

The initial biasing potential may be reduced by short-circuiting one of the resistor sections, such tern more sensitive and more readily responsive to changes in carrier wave strength at low amplitudes.

As the automatic volume control means is shown and described only by way of example and is not per se, part of the present invention, the same is believed to require no further description.

In accordance with the invention, the tuning indicator tube, indicated at 38, is arrangedl to receive signal indications through a separate intermediate frequency amplifier channel from Ythe Y signals applied to the second detector,r 8, and

from a point preceding the automatic volume Ycontrol. For this. purpose, the indicator tube 38 is preceded in the intermediate frequencyA amplifier channel by an intermediate frequencyA amplifier potential represented by the lead 52.

stage including the tube 39 and by a rectifier stage including the device 4U.

Theamplifler tube V39 is of the high gain,

pentode type, having av cathode 4I connected with Ytransformer 5I, and, together with the screen grid, .is connected to a positive source of anode Suitable filter resistors and by-pass capacitors, 53 and 54, respectively, are provided in circuit therewith.

The transformer 5I may be of the iron core k type and is sharply tuned to the intermediate frequency carrier wave to prevent the passage of Vsignals in a band wider than substantially ve diode rectiiiercircuit through the primary Winding 55. 'Ihe latter, together with a tuning capacitor 6 I, provides a sharply tuned input circuit for the rectifier.

The rectiiier 4l) may be an RCA GHG tube, and the remaining diode elements therein, as indi-- cated at 62, are connected to ground and are not used. The grounding connection serves to renderV them substantially ineffective in connection with the rectiiier circuit. Y l

The tuning indicator tube38 may be of the type known as thev RCA 6E5, which comprises a. target electrode which receives Yan electronic bombardment from a cathode 66 and fluoresces with a green light. The cathode is connected Vto ground through a lead' 61 andA a shield` wire.v 68.

surrounding a signal input lead 69. 'I'he input` lead 69 serves toconnect the control grid-10 of the tube with the diode output resistor 51 through a movable contact 1I thereon. The target 65 is connected through a lead 12 with` a positive'anode supply lead 52.

A i'ilter resistor 13. and by-pass capacitork 14 are providedv in connection with the lead 69, ad-

jacent to the contact 1I'. The filter resistor and.Y

capacitor provide a time delay means for preventing sudden changes in potential from causing too rapid change on the grid 10. 'I'he grid 10 is associated withthe cathode 66, and is further associated with an anode electrode 15 which is connected with the anode supply lead 12, through a series potential drop producing resistor 16.-

A gridwire1-1: extends from the anode 15 ,to` a position between the cathode 66: and a portion of the Screen or target 65, and casts an electronic.

shadowthereon, prevent-ing; theY electrons from reaching the target as the electrode 11' becomes more negative with respect to the target.

YThis condition; is controlled by'the'grid 16,;

which varies the anode current through the anode 15 and resistor 16,V an increasing negative potential on the Ycontrol grid 16, causing the anode current to be reduced and likewise the drop4 in potential through the' resistor 16. The electrode 11 is thereby permitted to approach the potential This is made a function of the strength of the received carrier wave by rectifying the carrier wave and applying the resulting direct current potential to the control grid through the filter In accordance with the invention, as shown in the present example, the carrier wave at intermediate frequency is applied to the pick-up coil 44 by coupling with the signal channel in the intermediate frequency ampliiier preceding the automatic volume control means or second detector, and for this purpose the coil 44 is coupled with and forms part of the intermediate frequency coupling transformer 1, thereby receiving energy from the secondary circuit comprising the Winding I4. The coupling is indicated in the drawing by the line connecting the two coils.

The carrier wave at intermediate frequency is amplified in the amplifier stage 3S and the amplified intermediate frequency carrier wave at the resonance frequency of the sharply tuned coupling transformer 5| is then applied to the rectifier 56-59. The direct current component of the rectified carrier wave is applied to the rectifier output resistor 51 to provide a biasing potential for the grid 10 of the indicator tube. lSince the cathode of the indicator tube is connected to ground, and therefore to the positive end of the resistor 51, the negative potential applied to the grid 10, with respect to the cathode 66, is determined by the position of the movable tap 1I.

In any given locality, depending upon the average strength of received signals, or dependent upon the sensitivity of the receiver resulting from aging of the tubes, the contact 1l may be adjusted to provide a sufficient negative potential on the grid 1D in the presence of a received carrier wave to just close the eye or provide a desired minimum shadow on the fluorescent target, for accurate tuning.

The device 1l, therefore, provides means for adjusting the sensitivity of the electronic, gridcontrolled indicator tube, while the sharply tuned intermediate frequency amplifier not only provides a strong, amplified signal for indicator purposes but provides this signal in a separate, sharply tuned channel which admits signals in a band of a predetermined width more narrow than that of the main signal channel for the second detector, resulting in a tuning indication at exact resonance.

Furthermore, by selecting the intermediate frequency energy or voltage from a point on the signal channel preceding the automatic volume control diode or rectifier device, which is also the second detector in the present example, the tuning indication remains substantially flat regardless of the strength of the received carrier wave.

However, since the control grid 43 of the indicator amplifier is connected with the automatic volume control circuit I8, exceptionally strong signals serve to control the gain of the amplifier in the same manner as the signal amplifier.

An advantage in this connection lies in the fact that the change in response effected by wave band change for the automatic volume control means is at the same time provided in the separate channel amplifier for the indicator tube, since the control grid 43 is under control of the automatic volume control means and operation of the sensitivity control switch 36.

In a receiver having X, A, B, C, and D bands, for receiving weather reports, standard broadcasts, police, short-Wave, and ultra short-wave signals, respectively, the switch 36 may be opened on bands X and A and closed on bands B, C, and D, to provide a greater sensitivity for the latter bands, thereby compensating for the lower carrier wave strength available in the reception of the .higher frequency signals. With this arrangement, the tuning indicator tube is substantially uniformly responsive, providing a sharp tuning indication for all wave bands.

In certain receivers the sensitivity of the indicator tube may be adjusted by providing a tap connection similar to the tap 1l in-connection with the wave band switch connection 31 as shown in Fig. 2 wherein the same parts and circuits have the same reference numerals as in Fig. l.

Referring to Fig. 2, the grid lead 69 for the indicator tube is connected indirectly with the tap 1l through the time delay filter 13-14 and an additional voltage divider resistor 80.

The voltage divider resistor 8i] is provided with a tap 8| for the lead 69 and is connected between the tap 1l and ground whereby the voltage available across the resistor 51 between the tap 'll and ground is applied to the resistor 80. A portion of this voltage is then available at the tap 8l serving to reduce the voltage on the indicator tube.

This reduced voltage is desirable for the normal broadcast or A band since the signal strength in that band is high. For the weaker signals in the B and C, bands, for example, the voltage may be increased to compensate by opening a switch 82 in ground connection for the shunt voltage divider 80, whereby the full voltage of the tap 1! is available for the control lead 63. The control of the switch B2 may be effected in any suitable manner as by the connection indicated whereby it is actuated in response to a wave band change.

I claim as my invention:

1. In a radio receiving system having a main signal channel, and a second detector and automatic volume control means connected therewith, the combination with an electronic tuning indicator device having a control grid, of a carrier wave rectifier device having an output resistor, means providing a variable tap connection for the control grid of the indicator device on said output resistor whereby a predetermined control potential may be applied to the indicator device, a tuned amplifier connected between said rectifier device and the main signal channel preceding the automatic volume control means and detector, said amplifier being more sharply responsive to signals than the main signal channel, and means for applying automatic volume control potentials to said amplifier.

2. In a multi-wave band radio receiving system having a main signal channel, and a second detector and automatic volume control means connected therewith, the combination with an electronic tuning indicator device having a control grid, of a carrier wave rectifier device having an output resistor, means providing a variable tap connection for the control grid of the indicator device on said output resistor whereby a predetermined control potential may be applied to the indicator device, a tuned amplifier connected between said rectifier device and the main signal channel, said amplifier being more sharply responsive to signals than the main signal channel, and means responsive to change in the frequency response range of the receiving system for effectively changing the control grid connection with said output resistor.

3. In a multi-wave band radio receiver, the combination with an intermediate frequency amplifier, of automatic volume controlv means responsive to received signals conveyed through said intermediate frequency amplifier, a tuning indicator device of the electronic grid-controlled type connected with said intermediate frequency amplier to receive signals therefrom at a point preceding said automatic volume control means, said connection including a high gain intermediate frequency amplifier, a rectifier device, and a sharply tuned iron core coupling transformer betweensaid amplifier and said rectifier device, means for deriving a biasing potential from said rectifier device for said tuning indicator device, and means for adjusting the value of vsaid potential in response to Wave band change.

4. In a multi-wave band radio receiving system having automatic volume control means,

' the combination with a tuned signal channel connected with said automatic volume control means to apply signals thereto, of resonance indicator means comprising a sharply tuned-signal amplier connected with said signal channel preceding i said automatic volume control connection, a diode rectifier connected with said sharply tuned signal amplifier to rectify signals therefrom, a diode output resistor in circuit therewith, a resonance indicator tube having a control grid variably Vconnected with said resistor to receive an adjustable biasing potential therefrom in response to received signals, and means for adjusting said potential to compensate for changes in sensitivity resulting from changes in wave band range of said receiving system.

5. In a multi-wave band receiver, the combination with automatic volume control means adjustable in sensitivity with wave band change, of

Y an intermediate frequency amplifier stage coupled to the signal channel of said receiver .preceding said automatic volume control means and being controlledthereby, a signal rectifier device, sharply tuned coupling means connected between said rectifier device and said amplier stage to apply signals to saidY rectifier device in a frequency band relatively narrow. with respect to the frequency response v'band of the signal channel of the receiver, a tuning indicator tube having a control grid coupled to said rectifier device to receive a portion: of the direct current potential therefrom resulting from signal rectification, and means for varying said last named coupling to control the sensitivity of said tuning indicator device in response to wave band change.

6'. VIn a multi-wave band receiver, the combination. with automatic volume control means ad-v justable in sensitivity with wave band change, of an intermediate frequency amplifier stage coupled to thel signal channel of said receiver precedingV said automatic volume control means and being controlled thereby, a signal rectifier device, sharply tuned coupling means connected between said rectifier device and said amplifier stage to apply signals to said rectier device in a frequency band relatively narrow with respect yto the frequency response band of the signal channel of the Vreceiver, a tuning indicator tube having a controlV grid coupled to said rectifier device to receive a portion of the direct current potential therefromV rsf 

